1. Field of the Invention
This invention relates to a grease composition and more particularly, to a heat-dissipating grease composition which is adapted for a long term use.
2. Description of the Prior Art
Heat-dissipating grease compositions are known including those compositions wherein there are used, as a base oil, dimethylpolysiloxane, dimethyldiphenylpolysiloxane, dimethyldecylmethylpolysiloxane and the like, to which thickening agents such as zinc oxide, alumina, aluminum nitride, boron nitride, carbon nitride and the like are added. These known compositions are described, for example, in, U.S. Pat. No. 3,885,984, Japanese Patent Publication No. 52-33272, Japanese Kokai Nos. 62-43492 and 62-43493 and Japanese Patent Application No. 63-307513.
These heat-dissipating greases are, however, disadvantageous in that the base oils have a great tendency toward creepage especially when the greases are used over a long term. This results in oozing out of the base oil around peripheral portions to which the grease has been applied. This may lead, for example, to oil contamination and particularly, contamination of nearby electric contacts or a portion between a commutator and a brush of a micromotor therewith, with the possibility of causing contact troubles and a failure in rotation of the micromotor. In addition, the creepage of the base oil gradually degrades the heat-dissipating characteristic.